The present embodiments relate to subterranean operations, and in some embodiments, to the use of nanoparticles in well bore cleaning.
A variety of drilling fluids have been used in drilling subterranean well bores. As used herein, the term “drilling fluid” may refer to any of a number of liquid and gaseous fluids, and/or mixtures of fluids and solids (e.g., solid suspensions, mixtures and emulsions of liquids, etc.) used in operations to drill well bores in subterranean formations. In some instances, a drilling fluid may be an aqueous-based fluid that comprises clays and/or polymers. During the drilling of a well bore in a subterranean formation, a drilling fluid may be used to, among other things, cool the drill bit, lubricate the rotating drill string to prevent it from sticking to the walls of the well bore, prevent blowouts by serving as a hydrostatic head to counteract the sudden entrance into the well bore of high pressure formation fluids, and remove drill cuttings from the well bore. A drilling fluid may be circulated downwardly through a drill pipe and drill bit and then upwardly through the well bore to the surface.
As the drilling fluid is circulated, a residue may be left behind on the surface of the well equipment and on the surface of the well bore itself. The residue may be referred to as a “filter cake” when formed on the walls of the well bore. The term “drilling fluid residue” as used herein may refer to the residue deposited on well equipment or on a permeable medium when a slurry, such as a drilling fluid, is forced against the equipment or medium while under pressure. Well equipment may comprise, but is not to be limited to oil and gas well, drilling, and completion equipment. Specific examples of well equipment may include pipe string, drill pipes, drill collars, drill bits, mud motors, directional drills, casings, liners, shakers, shaker screens, centrifuges, metal lines, fittings, impellers, and the like. Well equipment may not necessarily be in the well bore or used in the well bore when treated but may be treated at any time in conjunction with use in drilling or treating the well bore.
Once the well bore has been drilled to a desired depth, the drill string and drill bit may be removed from the well bore, and a pipe string (e.g., casing, liners, etc.) may be introduced into the well bore. After the pipe string is introduced into the well bore, the well bore may be conditioned by circulating the drilling fluid downwardly through the interior of the pipe string and upwardly between the annulus of the exterior of the pipe string and the subterranean formation. The purpose of this conditioning may be to remove as much of the drilling fluid residue from the well equipment and the walls of the well bore as possible. Unfortunately, at the end of this conditioning process, the drilling fluid residue may remain on the surfaces of the well equipment and the well bore. This may create problems with subsequent processing, such as in primary cementing operations. This incompatibility may result in a lack of bonding between the set cement composition and the surfaces in the well bore.
To mitigate the above-described problem, treatment fluids containing surfactants and other chemicals have been introduced into the well bore between the drilling fluid and the cement composition. The treatment fluid may be pumped ahead of the cement composition to help ensure effective mud removal and efficient cement placement. As the drilling fluid is displaced, the treatment fluid contacts the drilling fluid residue on the well bore and well equipment surfaces to at least partially remove the drilling fluid residue therefrom.
Additional cleanup issues may result from well equipment contacting tar and/or heavy oil during drilling operations. For example, many subterranean operations involve the drilling of a well bore from the surface through rock and/or soil to penetrate a subterranean formation containing fluids that are desirable for production. In the course of drilling operations and other subterranean operations, the drill string and/or other equipment and tools may come into contact with zones of rock and/or soil containing tar and/or heavy oil, such as heavy and light (liquid) hydrocarbons, asphalt, and bitumen; collectively referred to herein as “bituminous materials;” furthermore these zones are collectively referred to herein as “bituminous sand zones.” In many such operations, it may be desirable to drill the well bore through these bituminous sand zones. However, problems may be encountered when drilling through bituminous sand zones. For example, bituminous materials are typically tacky substances that may adhere to surfaces they contact. In addition, bituminous materials may dissolve into many types of treatment fluids used in the course of drilling operations, increasing the tackiness and adhesive properties of the bituminous materials. If a sufficient amount of bituminous materials adheres to surfaces in the well equipment, it may, among other problems, prevent the drillstring from rotating, prevent fluid circulation, increase non-productive time, create torque and drag issues, cause tool damage, or otherwise impede the effectiveness of a drilling operation. In some cases, it may become necessary to remove and/or disassemble the drillstring in order to remove accretions of bituminous materials, a process which may create numerous cost and safety concerns. The accretion of bituminous materials on drilling equipment and/or in the well bore also can impede any subsequent operations downhole, including cementing, acidizing, fracturing, sand control, and remedial treatments. In addition, soft, tacky bituminous materials that manage to reach the surface may foul surface equipment, including solids screening equipment and solids control equipment, for example, by binding shaker screens.
Existing methods of managing the problems that result from well bore bituminous material incursion may be problematic. Examples of conventional methods may utilize treatment fluids that comprise dispersants, surfactants, and/or solubilizers, which allow the bituminous materials to dissolve in or homogenize with the treatment fluids. However, the bituminous materials may not be readily separated out of the fluid once they have dissolved into or homogenized with the fluid. The presence of the bituminous materials in the treatment fluid may alter its rheological properties and/or suspension capacity, which may limit its use in subsequent operations. Moreover, the addition of these dispersants, surfactants, and solubilizers may increase the complexity and cost of the drilling operation.